add hid_composite_freertos example

examples/device/hid_composite_freertos/Makefile

@@ -0,0 +1,27 @@
+include ../../../tools/top.mk
+include ../../make.mk
+
+FREERTOS_SRC = lib/FreeRTOS/FreeRTOS/Source
+
+INC += \
+	src \
+	$(TOP)/hw \
+	$(TOP)/$(FREERTOS_SRC)/include \
+	$(TOP)/$(FREERTOS_SRC)/portable/GCC/$(FREERTOS_PORT)	
+
+# Example source
+EXAMPLE_SOURCE += $(wildcard src/*.c)
+SRC_C += $(addprefix $(CURRENT_PATH)/, $(EXAMPLE_SOURCE))
+
+# FreeRTOS source, all files in port folder
+SRC_C += \
+	$(FREERTOS_SRC)/list.c \
+	$(FREERTOS_SRC)/queue.c \
+	$(FREERTOS_SRC)/tasks.c \
+	$(FREERTOS_SRC)/timers.c \
+	$(subst ../../../,,$(wildcard ../../../$(FREERTOS_SRC)/portable/GCC/$(FREERTOS_PORT)/*.c))
+
+# FreeRTOS (lto + Os) linker issue
+LDFLAGS += -Wl,--undefined=vTaskSwitchContext
+
+include ../../rules.mk